Split-band heaters are well known in the prior art, and are used for many purposes, such as heating fluids within a tank, heating extruding nozzles of plastic injection apparatus, and many other uses. An early form of a split-band heater is shown in U.S. Pat. No. 1,614,330, issued to Edwin L. Wiegand, in which the heating resistor was embedded in compacted refractory material. The heater was manufactured as a rectilinear strip heater and subsequently formed to band shape. The split in this type of heater could be opened only a small amount because otherwise the compacted refractory material would develop cracks which result in hot spots in the heater and ultimate failure thereof. Therefore, this type of heater was largely confined to an assembly wherein the band could be slipped over an end of a cylindrical object.
Flexible strip heaters, such as shown in U.S. Pat. No. 2,817,742, issued to L. D. Drugmand were developed for the purpose of encircling a water tank, the rectilinear heater being insertable into a closed channel formed around the tank wall and the heater flexing to conform to the annular channel. In this case, mica was used as the insulating medium and this limited the heater to a relatively low heat. Further, because the design of the heater required flexibility, the channel in which the resistor and mica were disposed had a series of longitudinally-disposed slits through which moisture could enter.
A further development in the art is reflected in U.S. Pat. No. 3,730,373, issued to L. S. Kozbelt wherein two strip heaters, each of arcuate formation, were held around the wall of a cylindrical object by means of a separate clamping band. Although satisfactory in use, the cost of the clamping band, usually of stainless steel, was a disadvantage.
U.S. Pat. No. 3,619,566, issued to T. E. Finch, also discloses a development in the art. This patent eliminates the need for a separate clamping band, and enables the heater to be assembled transversely of a cylindrical object. The strip heaters in this patent had their opposite ends formed with hooks, the hooks at one pair of adjoining ends providing connection for a tensioning device and the hooks at the other pair of adjoining ends providing connection for an axially-slotted tubular spring member. However, reflexing the ends of the strip heaters is not an easy operation. Further, because the tensioning means, the two arcuate heaters and the tubular spring member are separate parts, it was difficult for one man to assemble the heater on a tubular object, especially the extruding barrel or nozzle of an injection molding machine.
My invention overcomes the disadvantages of the prior art, as above noted, and provides a low-cost split-band heater that is easily assembled around a cylindrical object by only one workman. My improved heater comprises two or more arcuately-shaped metal-sheathed heater sections, and hinge means between the sections and fixed thereto to become a part thereof, the hinge means enabling the heater sections to be sprung apart enough so that the heater may be positioned around a cylindrical object by movement transversely of the latter.
Each strip heater comprises an elongated metal channel having a planar base wall and a pair of coextensive sidewalls extending in the same direction from the edges of the base wall, the channel containing a resistance wire and electrical insulation means therefor, both disposed lengthwise within the channel. Each strip heater is arcuately bent so that its base wall is located innermost of the arc and adapted to fit along the curved transverse outer surface of the cylindrical object. The strip heaters are arranged in end-to-end relationship as longitudinal continuations.
A juxtaposed pair of spaced strip heater ends defining the split have the tensioning means connected thereto, the remaining juxtaposed pair of spaced ends being connected together by the flexible metal band. In one aspect of the invention, the heater sections share a common channel, with the sections spaced along the channel whereby in completed form the base wall of the channel provides a flexible strip between the heater sections to provide the hinge means.